SEOUL (AFP) - Five South Koreans held hostage in a Mexican border town for eight days have been released unharmed, the foreign ministry said Wednesday.

The ministry said all the abductees were Koreans. It could not immediately confirm a Yonhap news agency report that one was a Chinese national.

The group was seized on July 14 in Reynosa, a city on the US border in the state of Tamaulipas. One of the five had contacted family in Seoul, who in turn asked the foreign ministry for help.

The captives were freed at 7:00 pm Tuesday Mexico time (0000 GMT Wednesday), said Lee Jeong-Gwan, the ministry's director general for consular affairs.

"The Mexican police authorities applied strong pressure after identifying the captors, which appears to have led the gangsters to release them," Lee told a briefing.

The kidnappers had demanded a ransom of 30,000 dollars for the four men and one woman but nothing was paid, a foreign ministry official said.

Authorities are considering handing over the former hostages to their embassy after 48 hours spent investigating the case, the news agency said.

"We are not ruling out the possibility that they may have been attempting to illegally immigrate into the United States," the ministry official told AFP on condition of anonymity.

"If so, the case could be more complex than we had thought. But we cannot say anything for sure at the moment."

The kidnappers called police to inform them the Koreans had been released at a hotel in Reynosa. All were healthy.

Seoul thanked the Mexican government for its help in the release, which averts another potential overseas crisis.

South Korea is embroiled in a dispute with Japan after it reaffirmed its claims to disputed islands. It is also dealing with the aftermath of the killing of a South Korean tourist by a North Korean soldier.

Another group of South Koreans was kidnapped two years ago in Tijuana and later freed after a ransom was paid.

One year ago Taliban militants in Afghanistan kidnapped 23 South Korean church workers and murdered two of them before the Seoul government negotiated a release. There were unconfirmed reports that a large ransom was paid.

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